To remove the exhaust components, first disconnect the cable from the negative terminal of the battery, block the rear wheels, and set the parking brake. Raise the front of the vehicle securely on jackstands and remove the lower splash shield if equipped. Apply penetrating oil to the fasteners on the exhaust components and allow it to soak in before removing the exhaust Y-pipe from the vehicle. Disconnect the oxygen sensor connectors, and for G35 models, disconnect the lower steering joint at the steering gear and move the lower shaft aside to access the left-side manifold. Unbolt the exhaust heat shields and remove the catalytic converters from the exhaust manifolds by soaking and removing the bolts securing the front of the converters. When removing the left exhaust manifold on G35 models or either manifold on 350Z models, drain the coolant and remove the coolant tube from the front and sides of the engine. Finally, remove the manifold-to-head nuts/bolts and detach the manifold and gasket. For installation, use a scraper to remove all traces of old gasket material and carbon deposits from the mating surfaces of the manifold and
Cylinder Head. Position the new exhaust manifold gaskets over the studs on the cylinder head, ensuring the marked arrow or large dot points up when installed. Install the manifold and thread the mounting nuts/bolts into place, then tighten them in several increments to the specified torque. Reinstall the remaining parts in the reverse order of removal and run the engine to check for exhaust leaks.